Rotary valve actuators are used to actuate valves which must be rotated from an open position to a closed position. In any application in which fluids are conveyed through conduit, such rotary valves are positioned in tubular valve housings which are incorporated into the conduit. In such installations, the valve actuators are secured to an exterior surface of the tubular valve housings. The valve actuators have at least one male member which extends through an aperture in the tubular valve housings to engage the valve. The valve is actuated by rotation of the male member. The rotation of the male member, in turn, rotates the valve between the open position and the closed position.
A particularly onerous application for a rotary valve actuator is the operation of a kelly valve on a drilling rig drilling oil and gas wells. In such applications, the valve is subjected to a flow of abrasive and corrosive drilling fluids. The valve is also subjected to jarring impacts which are transmitted from the drilling bit, up the length drill string to the kelly. These harsh conditions lead to inconsistency in operation of the rotary valve actuator. Exposure to such corrosive drilling fluids makes the valve increasingly difficult to rotate between the open position and closed position as drilling procedures continue. Some rotary valve actuators are unable to generate sufficient foot pounds of torque to completely close the valve, as corrosion affects the operation of the valve. Some rotary valve actuators have a tendency to close prematurely when subjected to a jarring impact.